Fluorometric determination and intracellular imaging of cysteine by using glutathione capped gold nanoclusters and cerium(III) induced aggregation.

A turn-on fluorometric method is described for selective and sensitive detection of cysteine (Cys). Gold nanoclusters (Au NCs) capped with glutathione (GSH) are used as a fluorescent probe. If Ce3+ ion are present, they will bind to the carboxy groups of the GSH-capped Au NC. This results in aggregation-induced emission enhancement (AIEE), best measured at excitation/emission wavelengths of 360/575 nm. On addition of Cys, which has less steric hindrance compared with GSH and higher affinity for Ce3+, it will bind to Ce3+ through the carboxyl group and link with Au NCs via Au-S bond. Hence, the AIEE is increased and Cys can be quantified via this effect with a linear response in the 0.4-120 μmol L-1 Cys concentration range and a detection limit of 0.15 μmol L-1. Graphical abstract Schematic presentation of cysteine detection via the Ce3+-triggered aggregation of glutathione capped gold nanoclusters which leads to increased yellow fluorescence.